A resumable two-photon fluorescent probe for Cu 2+ and S 2- based on magnetic silica core-shell Fe 3 O 4 @SiO 2 nanoparticles and its application in bioimaging.

A two-photon fluorescent probe for Cu ²⁺ and S ^2- has been strategically prepared with naphthalimide derivative platform (NPE) covalently grafted onto the surface of magnetic core-shell Fe ₃ O ₄ @SiO ₂ nanoparticles. The probe (NPE-Fe ₃ O ₄ @SiO ₂ ) exhibits selective response to Cu ²⁺ with enhanced fluorescence and efficient separation of Cu ²⁺ with external magnetic field. The consequent product NPE-Fe ₃ O ₄ @SiO ₂ -Cu of NPE-Fe ₃ O ₄ @SiO ₂ and Cu ²⁺ can work as an excellent sensor for S ^2- by removing Cu ²⁺ from the complex with fluorescence decreased, recovering the fluorescence of the probe. Therefore, the constituted Off-On-Off type fluorescence monitoring system means the probe is resumable. Moreover, the probe has been used to quantitatively detect Cu ²⁺ and S ^2- with low detection limits, which are 0.28 μM and 0.12 μM, respectively. Furthermore, the probe shows low cytotoxicity and excellent membrane permeability, which has been successfully applied for monitoring Cu ²⁺ and S ^2- in living cells and imaging Cu ²⁺ in deep-tissue with two-photon excited fluorescence.
(Copyright © 2018. Published by Elsevier B.V.)